1. Field of the Invention
The present invention relates to analog-to-digital conversion technique, especially to the technique of successive approximation analog-to-digital converter and conversion method.
2. Description of Related Art
A successive approximation analog-to-digital converter is operable to carry out a binary search to an analog input signal in accordance with every available quantization level of the converter itself, and thereby generate a digital output signal. Among all kinds of successive approximation analog-to-digital converters, a charge redistribution successive approximation analog-to-digital converter is a common choice for actual implementation. This kind of converter samples an analog input signal through a capacitor array, and connects the bottom electrodes of a plurality of capacitors in the capacitor array with a reference voltage in an order conforming to the capacities of these capacitors and a comparison result after the sampling finishes, so that the voltages outputted by the capacitor array (i.e. the voltages of the top electrodes of the plurality of capacitors) will vary due to the conservation of charges. Afterwards, the converter will compare the voltages outputted by the capacitor array with the output voltages of another capacitor array or a constant voltage to generate the aforementioned comparison result, and thus generate a digital output signal according to the comparison result.
To a device (e.g. an image decoder) using the above-described charge redistribution successive approximation analog-to-digital converter, if the peak value of the said analog input signal (e.g. an image signal) goes beyond the quantization resolution of this analog-to-digital converter, the digital output signal generated thereafter will lack fidelity. Accordingly, the current art makes use of a programmable gain amplifier (PGA) to adjust the peak value of the analog input signal, so as to prevent the problem of fidelity loss. However, since a programmable gain amplifier has the features of large circuitry area and high power consumption, the adoption of such an amplifier will lead to the problems of cost increase and power consumption; as a result, this technique field still needs a better solution capable of preventing fidelity loss while giving consideration of cost control and power saving.